Final answer:
Option 3: The skirt sways around them.
The skirt sways around the person when they move their hips, as this is how clothing generally responds to movement. It's a physics-based reaction that's observed naturally, similar to fringes swaying described in a running woman's silhouette.
Step-by-step explanation:
When a person moves their hips while wearing a red skirt, the most natural outcome is that the skirt sways around them. This is a simple matter of physics and the way that clothing behaves in response to movement. Neither changing color nor becoming tight is a standard response to the movement of hips, and stumbling would typically only occur if the skirt were improperly fitted or if there was an external factor causing the person to trip. The motion of the skirt can be likened to the fine fringes described as falling from the outstretched arms of a running woman's silhouette, evoking a sense of freedom and ease in movement.